As a measurement instrument for measuring a surface profile, dimensions and the like of a measurement target, a measurement instrument configured to perform a calibration processing using a step gauge having reference measurement surfaces at every predetermined interval has been typically known (Patent Literature 1: JP2004-125665). In such a measurement instrument, calibration of dimensions can be conducted by measuring each of the reference measurement surfaces provided at every predetermined interval in the step gauge.
Such a step gauge typically includes: measurement blocks (end standard) each having reference measurement surfaces; and interval blocks each interposed between a pair of ones of the measurement blocks to keep a distance between the pair of ones of the measurement blocks strictly at a set distance, the measurement blocks and the interval blocks being alternately coupled one by one.
The above-described step gauge is required to exhibit an extremely small change in dimensions caused by a change in environments under which the step gauge is used and a change over time, because the step gauge is intended for calibration of the measurement instrument.
In recent years, there has been used a step gauge including the measurement blocks and the interval blocks made of an ultra-low expansion material in order to inhibit the change in the dimensions of the measurement blocks and the interval blocks caused by a temperature change.
However, even when the blocks are made of the ultra-low expansion material as described above, if a coupler coupling the blocks has a large coefficient of linear thermal expansion, a stress for coupling the blocks may be changed due the temperature change, which may change the dimensions of the entire step gauge.